The surface of a substrate, for example paper or cardboard, consists of an interwoven web of wood fiber. This web of interwoven fibers is visible when looking through the paper with an illuminated background. The patterns formed within the web of wood fiber are largely random, which causes each different substrate, for example each sheet of paper, to have a unique microstructure. This unique microstructure cannot be replicated from the substrate, thereby giving each substrate a unique identity.
The possibility of identifying each document uniquely, paves the way for authentication of products, documents, objects and articles by analyzing inhomogeneous and ‘random’ microstructures of the paper, also known as the “signature” of the product, document, object, or article. Since the signature contains the document's unique characteristics, it cannot be transferred to other documents, and this data cannot be easily stolen or given away to others.
Authenticating the unique identity of documents provides security for the consumer and protection for the manufacturer. The problem of counterfeiting is much more relevant in today's world than it has been at any time in the past. Counterfeit duplication of documents has grown in all industries, including the health industry, financial industry, and safety industry. With advancement in counterfeiting technologies, particularly the increased resolution and reduced cost of scanning and printing technologies, the counterfeiting problem is rapidly increasing.
Currently, there are numerous systems for authenticating documents, ranging from techniques that attempt to measure the randomness of ink splatters made by a printer to extract a unique sign, or measure randomness of fiber structure, to use of scanners to model 3D fiber structure, or lasers to model surface scattering, or use microscope to capture texture information from document.
One particular authentication technology, known as “Fiberfingerprint” technology, employs custom based device to authenticate documents by capturing naturally occurring irregularities of a substrate as a means to discriminate between various documents or objects. The system uses registration marks to identify the area of the medium that should be analyzed. For imaging, a consumer-grade video module and lens, along with the appropriate lighting apparatus, is used to capture the analysis area, which is stored to an online server. To authenticate the document, the analysis area is imaged with a laser microscope to capture the irregularities, and the imaged area is compared with the image stored on the online server. Laser surface authentication technology, however, requires an expensive laser microscope and special imaging setup to capture irregularities in paper, which might restrict its usage among users. Additionally, the Fiberfingerprint technology requires the verifier to be online to match the signature, which limits the utility and the locations at which the technology can be used.
Another conventional authentication technology utilizes scanner technology for document authentication. For example, mid-range scanners can be used to model the three-dimensional (3D) fiber structure of a paper and generate unique fingerprints based on it. The original document is scanned several times at different orientations to produce an estimate for the 3D surface texture of the document. The features obtained are reduced to a concise feature vector, which is encrypted and printed on the document. This scanning technology is robust, but requires use of bulky equipment, which restricts portability of the system. Another conventional scanning authentication technology uses a commodity scanner and laser to identify documents. Such a system is less robust than the 3D scanning technology, but is still not very portable.
Another conventional authentication system, known as “PaperSpeckle,” leverages the natural randomness property present in paper to generate a fingerprint for any piece of paper. The phenomena of multiple scattering of partially coherent light (natural light) from the complex microscopic structure (surface irregularities and particles) of the paper region is captured using a microscope to obtain the texture speckle pattern and use this information to produce a unique fingerprint of a region of the document. The Gabor transform and a Singular Value Decomposition (SVD) are used to obtain eigenvalues (or singular values) of the Gabor transformed speckle and generate a fingerprint for a speckle pattern. The PaperSpeckle system, however, requires a microscope, which is not readily available to an end user. Moreover, the requirement of a microscope significantly increases the cost of the verification system.
Other conventional authentication systems include securing products using special inks, anti-copying visible patterns, or embedded holograms or microtext. A document fingerprint can be produced from the random ink splatter that occurs around the edges of any features printed on a page. Given a document to be protected, the secure pattern is printed onto a blank area of the paper. Additionally, several auxiliary landmarks may also printed around the pattern to facilitate alignment. The authentication then requires examination by a microscope. One problem with this this approach is that it can only be applied after a document has been printed. Moreover, this method requires modification of original document for printing a predetermined pattern. Additionally, the method also requires use of microscope, which, as discussed above, may not be available and can be expensive for the end user.
Most of the conventional techniques discussed above are expensive, for example requiring expensive equipment to perform a validation of a document. As a result, the applications for which these methods can be used are restricted, and may not be available in certain locations or industries due to prohibitive costs. Moreover, some of these authentication technologies require modifications of the product, which are generally not desirable. What is needed, therefore, is a robust authentication system that minimally modifies the product, does not require expensive equipment, and is widely usable in a variety of applications.